This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In the past year, we studied the considerable individual variation in the propensity to form a partner preference and to display paternal care among male prairie voles. Unlike most mammalian species, prairie voles (Microtus ochrogaster) are socially monogamous. We have found that prairie voles are a powerful model species to investigate the neurobiological mechanisms underlying variation in social behavior. We have found that the vasopressin V1a receptor (V1aR) plays a central role in both pair bond formation and paternal care in the male prairie vole. Variation in both of these behaviors has been associated with variation in V1aR density in several brain regions, including the lateral septum (LS). The goal of this project is to explore how variation in V1aR density in the LS leads to within-species diversity in male social behavior. First, an siRNA approach was utilized to knock-down V1aR density in the LS. siRNA injected voles have been tested and compared to controls for their propensity to form a partner preference and to engage in paternal behavior. We have been proceeding in developing a selective breeding strategy to determine whether V1aR density in the LS is a major source of heritable variation in social behavior. Once the lines are established, the density of V1aR binding in the LS and other brain regions will be quantified.